1. Field of the Invention
This invention relates to a planetary gear type forward and backward drive switching apparatus for a vehicle comprising first and second running line transmission shafts for transmitting output of an engine to running means disposed coaxially each other, a sun gear mounted on the first running line transmission shaft, a carrier mounting planetary gears meshing the sun gear and rotatable about the transmission shafts, a ring gear meshing the planetary gears and rotatable about the transmission shafts, and friction brake means for selectively braking rotations of the carrier and the ring gear, and clutch means for selectively transmitting rotational outputs of the carrier and the ring gear to the second transmission shaft, and more particularly to said apparatus included in a transmission system having a main transmission, an auxiliary transmission, an axle transmission mechanism and power takeoff means.
This forward and backward drive switching apparatus is adapted for selectively transmitting a rotational power of the sun gear to the running line transmission shaft in a normal rotation or in a reverse rotation through braking switching operations by the friction brake mechanism and engagement switching operations by the clutch mechanism.
2. Description of the Prior Art
This type of forward and backward drive switching apparatus is disclosed, for example, in a Japanese utility model application published or laid open for public inspection under No. 58-36651. According to the disclosed arrangement, the friction brake unit is disposed between peripheral faces of the ring gear and the carrier such that the brake as a whole selectively acts on an inner peripheral face of the ring gear and an outer peripheral face of the carrier. This arrangement has disadvantages to be described hereinafter.
If the brake as a whole has to act on the overall or substantially overall peripheral faces of the ring gear and the carrier in order to obtain a secure braking effect, it is necessary to adapt the main brake body to variably have a large radius and a small radius to respectively act on one or the other of the ring gear and the carrier. Thus, the main brake body need be structually complicated including a large number of parts.
Moreover, the simplification of the structure and the minimization of the occupying space are requisite for accommodating this type of forward and backward drive switching apparatus in the transmission system including the main transmission, the auxiliary transmission, the axle transmission mechanism and the power takeoff means. Also, it is needless to say that the structures and arrangements of the main transmission, the auxiliary transmission, the axle transmission mechanism and the power takeoff means must be improved in order to form the system as a whole compact.